Broad-band antenna



Nov. 2, 1948. J. D. KRAUS BROAD-BAND ANTENNA Filed April 2; 1946INVENTOR JOHN 0. KRAus A T TOPNEY Patented Nov. 2, 1948 BROAD-BANDANTENNA John D. Kraus, Newton Center, Mass'., assignor to the UnitedStates of America as represented by the Secretary of War ApplicationApril 2, 1946, Serial No. 658,942

Claims. 1

This invention relates generally to electrical apparatus and moreparticularly to antennas.

Frequently, in antenna applications, some of the characteristics ofantennas may be of greater importance than others. For example, a givenantenna application may require that the antenna be operable overextremely wide ranges of frequences, even at the expense of antennadirectivity.

In antenna applications, where directivity may be sacrificed in favor inbroad-band characteristics, some antennas of the prior art have beenused over fairly wide ranges of operating frequencies. However, theresponse or radiation patterns of these antennas usually split into aplurality of secondary lobes as the operating frequency is varied.

In many antenna installations, where broadband antenna characteristicsare required, it is desirable only that the antenna patterns remaingenerally directional as the operating frequency is varied. Antennaapplications requiring a narrow and precise pattern have become numerousin recent years, however there still remain many antenna applicationsfor which antennas having a fairly broad-beam width are more desirable.

It is an object of the present invention to provide a very broad-banddirectional antenna.

It is also an object to provide a broad-band antenna whose major loberetains its original direction of maximum response or radiation as theoperating frequency is varied over wide ranges.

Generally this invention comprises a dipole antenna and a cornerreflector. The corner reflector consists of two sides, a top and abottom. A center fed radiating element is inserted in the cornerreflector with the ends of the element in contact with the top andbottom plates of the corner reflector.

ther objects, features and advantages "of this invention will suggestthemselves to those skilled in the art and will become apparent from thefollowing description of the invention taken in connection with theaccompanying drawing in which:

Fig. l is an isometric view of an antenna embodying the principles ofthis invention;

Fig. 2 is a sectional view of Fig. 1 taken at section 2-2 shownschematically;

Figs. 3 and 4. are antenna patterns obtainable by the antenna shown inFig. 1.

Referring now to Fig. 1, a center fed radiating element consisting ofupper and lower sections i8 and H, is inserted in a corner reflector.The

axis of the antenna is contained in a plane which bisects the includedangle between sides l2 and E3 of the corner reflector. tact with the topplate l4 and section H is in contact with the bottom plate [5 of thecorner reflector. A coaxial feed line consisting of inner conductor l6and outer conductor ll enters the corner reflector through a hole inbottom plate l5 and is coaxially inserted in section II. conductor l6terminates in contact with the tapered end of section l0, and outerconductor I'l terminates in contact with the tapered end of section ll.

Fig. 2 shows the connections of the radiating elements it and II to theinner, and outer conductors l6 and ll of the coaxial line.

Fig. 3 shows the horizontal pattern it of a vertically polarizedantenna-reflector system when the length L, Fig. 2, corresponds toapproximately one-half of a Wavelength or more of the operatingfrequency.

Fig. 4 shows the horizontal pattern comprising lobes i8 and it of avertically polarized antennarefiector system when the length L, F g. 2,corresponds to approximately one-quarter of a wavelength or less of theoperating frequency.

Referring again to Fig. 1, this assembly operates at high frequenciessimilarly to a conventional dipole-reflector. When the operatingfrequency is such that the length of the element is of the order ofone-half of a wavelength orv 7 ing frequencies are used, so that thelength of the element is of the order of one-quarter of a.

wavelength or less, the bidirectional antenna pattern shown in Fig. 4 isobtained. At these lower operating frequencies, the element togetherwith the reflector, operates similar to a conventional loop antenna,resulting in the familiar bidirectional pattern of Fig. 4.

At the lower frequencies, the existence of the rear lobe l9, Fig. 4, mayor may not be undesirable. The pertinent fact is that the main forwardlobe I8 is still retained and that its axis has not been shifted,

At the center of the radiating element, the ends of the upper and lowersections it and H are tapered to improve the impedance match between thecoaXial feed line and the antenna assembly.

The included angle formed by the intersection of the two sides of thecorner reflector is not critical and is determined by the desiredbandwidth of the antenna pattern.

Section i0 is in con-- Although a corner reflector has been shown as apart of the combination, by way of example, reflectors of otherconfigurations can be used. For instance, the reflector surfaces i2 and53 may of cylindrical or parabolic shape instead of flat surfaces as inFig. 1.

While there has been here described What is at present considered to bethe preferred embodiment of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the scope of the invention.

What is claimed is:

1. A broad-band vertically polarized antenna assembly including ametallic corner reflector having two sides which meet to form a corner,a bottom and a top inclosing said corner, a center fed radiatingelement, said element comprising two linearly arranged radiatingsections each having a large diameter, the adjacent ends of saidsections being tapered to a smaller diameter, said element beingvertically oriented within said reflector so that the longitudinal axisof said element lies in a plane which bisects the included angle formedby the intersection of the two sides of said reflector, the outer endsof said sections terminating in electrical contact with the top andbottom of said reflector, and a coaxial feed line inserted through ahole in the bottom of said reflector and coaxially enclosed within thelower section of said element with its inner conductor terminating inelectrical contact with the tapered end of the upper section of saidelement and with its outer conductor terminating in electrical contactwith the tapered end of the lower section of said element.

2. A broad-band plane polarized antenna assembly including a verticalcorner reflector having a pair of side plates which meet to form acorner and a bottom plate and a top plate inclosing said corner, acenter fed radiating element vertically oriented in said reflectoradjacent the corner thereof with the ends of said element electricallyconnected to the top and bottom plates of said reflector whereby asharply defined unidirectional antenna pattern is obtained when thelength of said element corresponds to approximately one-half of awavelength or more of the operating frequency and a bidirectionalantenna pattern is obtained when the length of said element correspondsto approximately one quarter of a wavelength or less of the operatingfrequency.

3. A broad-band antenna assembly comprising a corner reflector having apair of side surfaces which meet to form a corner with bottom and topsurfaces inclosing said corner, and a center fed linear radiatingelement disposed within said reflect-or, said element being arranged sothat the longitudinal axis thereof has in the plane which bisects theangle between said sides, the opposite ends of said element beingelectrically connected to said top and bottom surfacs.

4. A broad-band antenna assembly comprising a corner reflector having apair of side surfaces which meet to form a corner with top and bottomsurfaces inclosing said corner. center fed radiating element within saidreflector, said element including two linearly arranged radiatingsections, said element being disposed so that the longitudinal axisthereof lies in the plane which bisects the angle between said sidesurfaces, the opposite ends of said sections terminating in electricalcontact with said top and bottom surfaces, and a transmission lineconnected to the adjacent ends of said sections for feeding saidelement.

5. A broad-band antenna assembly comprising a corner reflector havingtwo side surfaces which meet to form a corner with top and bottomsurfaces inclosing said corner, a center fed radiating element withinsaid reflector, said element having two linearly arranged radiatingsections, each section having large diameter, the adjacent ends of saidsections being tapered to a relatively small diameter, said elementbeing disposed so that the longitudinal thereof lies in the plane whichbisects the angle between said side surfaces, the outer ends of saidsections terminating in electrical contact "ith said top and bottomsurfaces, and a transmission line connected to the adjacent ends of saidsections icifeeding said element. 7

J OHN D. KRAUS.

